Arithmetic Micro-operations of 8085 microprocessor

A micro-operation is an elementary operation performed with the data stored in register. The micro-operation most often encountered in digital computers are classified into four categories.

• Register transfer micro-operations transfer binary information from one register to another register .
• Arithmetic micro-operation perform arithmetic operations on numeric data stored in registers.
• Logical micro-operation perform bit manipulation operation on non-numeric data stored in register
• shift micro-operations perform shift operations on data stored in register.

The register transfer micro-operation was introduced in our previous post. This type micro-operation does not change the information content when the binary information moves from the source register to destination register. The other three type of micro-operations change the information content during the transfer. In this post we introduce a set of arithmetic micro-operations.
the basic arithmetic micro-operations are addition,subtraction,increment,decrements,and shift. Arithmetic shifts are explaining later in the conjunction with the shift micro-operation. The arithmetic micro-operation define by the following statement :

                                           R3 <- R1 + R2

Add micro-operation :  Specifies an Add micro-operation. it state the content of register 1 (R1) are added to the content of register R2 and the sum transfer to the register R3 .To implement this statement with hardware we need three register and the digital components that performs the addition operation. The other basic micro-operation are listed in Table - 1.

Subtract micro-operation : Subtraction is most often implemented through complementation and addition. Instead of using the minus operator , we can specify the subtraction by the following statement :
                                                               
                                        R3 <- R1 + R2 + 1  
    
R2 is the symbol for 1's complement of R2. Adding 1 to the 1's complemnt produce the 2's complement. Adding the content of R1 to the 2's complement of R2 is equivalent to R1 - R2 .


                                   TABEL - 1 Arithmetic Micro-operation .